1. Field of the Invention
This invention relates to an improved method for the production of carbon dioxide sorbents, and more specifically, this method relates to a method to produce amine-based sorbents for use to extract CO2 from utility effluents.
2. Background of the Invention
Separation and capture of carbon dioxide (CO2) have been identified as a high-priority research topic in Department of Energy (DOE) reports. The costs of separation and capture, including compression to the required pressure for the sequestration step, are generally estimated to comprise about three-fourths of the total cost of ocean or geologic sequestration. An improvement of the separation and capture of CO2 will reduce the total cost required for sequestration.
The most likely options for CO2 separation and capture include chemical absorption, physical and chemical adsorption, low-temperature distillation, gas-separation membranes, mineralization/biomineralization, and vegetation. The CO2 absorption process employing aqueous amine solutions (i.e., wet chemical stripping) have been used for the removal of CO2 from gas streams in some industries. This process, based on the principles of chemical absorption of CO2 via monoethanolamine (MEA) or diethanolamine (DEA), is a potential technique for capturing greenhouse gas emissions from flue gas streams.
Wet chemical stripping of CO2 involves one or more reversible chemical reactions between CO2 and another substance such as MEA to produce a liquid species, such as a carbonate. Upon heating, the carbonate (heretofore isolated from the CO2 feed stream) breaks down to free CO2, with the original amine regenerated to react with additional CO2. An example of the process, with monoethanolamine, is:
Another proposed reaction sequence has been identified by Hook, R. J., Ind. Eng. Chem. Res., 1997, 36, 1779-90, and which is shown below as Equation 2.
These carbon dioxide capture and regeneration methods require high temperatures or very low vacuum. The process is complicated, costly, and energy intensive. Further, the amine solution has a limited lifetime due to degradation through oxidation of the amine. In addition, corrosion problems are usually seen in the aqueous amine process. Water usage is excessive due to the mechanism, corrosiveness, and air flow problems created by the use of amines such as MEA and DEA.

Solid amine-immobilized sorbents have the potential of reducing corrosion, energy cost, application of corrosion inhibitors, and mass heat transfer problems inherent with liquid capture systems. As a result, immobilized amine sorbents (IAS) are being used in controlled environments such as aircraft, submarine, and spacecraft. However, the cost of these sorbents is too expensive for large-scale applications in the utility industry.
Aqueous CO2 capture systems use primary, secondary, and tertiary alkanol-amines to transform CO2 into bicarbonate. These liquid amine systems require two moles of amine to one mole of CO2 for the formation of stable bicarbonate compounds.
U.S. Pat. No. 3,491,031 awarded to Stoneburner on Jan. 20, 1970 discloses a method to create a CO2 sorbent by treating activated carbon with gaseous alcohol amines such as MEA. It utilizes a wet-chemical stripping method employing MEA to remove the adsorbed CO2 and regenerate the sorbent.
U.S. Pat. No. 6,547,854 awarded to Gray et al., on Apr. 15, 2003 discloses a method to create solid CO2 sorbents by the treatment of an acidified or basified solid substrate with a substituted amine salt.
U.S. Pat. No. 6,364,938 awarded to Birbara et al. on Apr. 2, 2002 discloses a method to create CO2 sorbents by the incorporation of amine groups into a polymer substrate or backbone. The method is applicable to low load situations such as human breathing environments.
U.S. Pat. No. 6,755,892 B2 awarded to Nalette, et al. on Jun. 29, 2004 discloses a CO2 absorbing method wherein sorbent beds are cycled between absorbing CO2 and desorbing CO2.
U.S. Pat. No. 5,876,488 awarded to Birbara et al. on Mar. 2, 1999 discloses a method to create CO2 sorbents by dispersing aqueous amines in polymeric materials. Such sorbents are limited in application to human breathing environments and at ambient temperatures of 25° C.
U.S. Pat. Nos. 5,620,940, 5,492,683 and 5,376,614, all awarded to Birbara et al. disclose methods to create CO2 sorbents by using amine-polyols on chemically inert supports. Sorbent desorption methods employ heat and/or reduced pressure.
U.S. Pat. No. 4,810,266 awarded to Zinnen, et al. on Mar. 7, 1989 discloses a method to create CO2 sorbents by treating carbonized molecular sieves with alcohol amines.
A need exists in the art for a method to produce amine-enriched sorbents for the capture of CO2 from high-output fluids such as flue gas and natural gas streams. A need also exists for a sorbent that does not require energy-intensive use of water during CO2 capture processes and which retains CO2 over a range of operating temperatures. The sorbent should be thermally stable and easily regenerated.